AD7827 Analog Devices, AD7827 Datasheet - Page 9

• Manufacturer Part Number: AD7827
• Description: 3/5V, 1 MSPS, 8-Bit, Serial Interface Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7827

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 1MSPS
• Interface: Ser
• Analog Input Type: SE-Uni
• Ain Range: Uni 2.0V,Uni 2.5V
• Adc Architecture: Pipelined
• Pkg Type: DIP,SOIC

OPERATING MODES
The AD7827 has two possible modes of operation depending on
the state of the CONVST pulse at the end of a conversion.
Mode 1 Operation (High Speed Sampling)
When the AD7827 is operated in Mode 1 the device is not
powered down between conversions. This mode of operation
allows high throughput rates to be achieved. Figure 13 shows
how this optimum throughput rate is achieved by bringing
CONVST high before the end of the conversion. When operat-
ing in this mode, a new conversion should not be initiated until
30 ns after the end of a read operation. This is to allow the
track/hold to acquire the analog signal to 0.5 LSB accuracy.
REV. 0
CONVST
CONVST
SCLK
SCLK
D
D
RFS
RFS
OUT
OUT
t
POWER-UP
t
1
Figure 13. Mode 1 Operation Timing Diagram
Figure 14. Mode 2 Operation Timing Diagram
t
2
t
2
A
CURRENT CONVERSION
CURRENT CONVERSION
B
–9–
RESULT
RESULT
Mode 2 Operation (Automatic Power-Down)
When the AD7827 is operated in Mode 2 (see Figure 14) it
automatically powers down 530 ns after the falling edge of
CONVST. The CONVST signal is brought low to initiate a
conversion and is left logic low until 530 ns has elapsed after the
falling edge of the CONVST pulse, i.e., before Point A or Point
B in Figure 14, depending on the actual value of t
Characteristics). The state of the CONVST signal is sampled at
this point (i.e., 530 ns after CONVST falling edge) and the
AD7827 will power down as long as the CONVST is low. The
ADC is powered up again on the rising edge of the CONVST
signal. The CONVST pulse width does not have to be as long as
the power-up time if an external reference is used (see Power-Up
Times section). Superior power performance can be achieved in
this mode of operation by powering up the AD7827 to only
carry out a conversion. The serial interface of the AD7827 is
still fully operational while the device is powered down.
AD7827
2
(see Timing